Dewaxing of mineral oils



Patented June 6, 1939 PATENT OFFICE DEWAXING OF MINERAL OILS Edwin C.Knowles, Beacon,

The Texas Company, poration of Delaware N. Y., assignor to New York, N.Y., a cor- No Drawing. Application January 27, 1938, Serial No. 187,161

4 Claims.

This invention relates to the dewaxing. of hydrocarbon oil, andparticularly to the separation of wax from a mineral lubricating oil.

The invention contemplates the separation-of wax from ployment of a waxcrystal modifying material to facilitate dewaxing by filtration,centrifuging or cold settling. The use of various crystal modifiers indewaxing processes employing a diluting or dewaxing solvent hasheretofore been suggested. These suggested modifiers include metalsoaps, such as aluminum stearate, and various esters, such as glyceroland glycol stearates. Certain monosaccharose and disaccharosederivatives of aliphatic acids have also been suggested as pourdepressants for mineral oil; and by analogy from the wax crystalmodifying effect of pour depressants, the use of these materialsasdewaxing aids might be reasoned.

In commercial dewaxing plants employing dewaxing solvents, it is founddifficult if not economically impossible to maintain the solvent of thesystem in an anhydrous condition, the solvent frequently containing asmuch as /2% or more of water. -It is found that the majority of dewaxingaids, such as those mentioned above, lose at least a substantial part oftheir, effectiveness in the presence of wet solvent. Moreover, due tohydrolysis in the presence of the wet solvent, suchaids result in objectionably raising the saponification number and the neutralizationnumber of the dewaxed oil. Other dewaxing aids of the character ofasphaltenes, petroleum residuums, coil tar fractions and the like causean objection-discoloration of a pale oil being dewaxed.

In accordance with the present invention, there is used as a wax crystalmodifying material in the dewaxing of mineral oil a higher fatty acidester of a polysaccharide of the general formula (Cal-11105011., where nis a large number. Polysaccharides contemplated herein in.- cludecellulose and starch. The fatty acid radical or radicals are preferablystearates, palmi- 45 tates, oleates, and other higher fatty acids ormixtures thereof. These esters of the polysaccharides are found topossess unusual effectiveness as dewaxing aids and overcome objectionsof the esters and related compounds speci- 50 fled above which haveheretofore been suggested for this purpose.

The esters of the polysaccharides may be employed alone as dewaxingaids, but they are preferably used in conjunction with montan wax or 55a material analogous in its properties to montan such a wax bearing oilby the emwax. Where the expression montan wax is employed herein, it isto be understood that this refers to the crude montan wax or to theactive ingredients which may be extracted or otherwise separated fromcrude montan wax. The acid treated or bleached. .and refined montan waxis comparatively ineffective for this purpose. The dewaxing aid ispreferably employed in a proportion of less than 1% by weight on theweight of the wax bearing oil charge. Where the polysaccharide. ester isused alone, satisfactory results may be secured with a proportion ofabout 0.150.50%, with a proportion of around 0.25% being preferred.Where the polysaccharide e..- ter is used in conjunction with montanwax, a proportion of 01-05% of theester together with about 0.02-0.20%of montan wax gives satisfactory results, with a proportion of about0.2% of the ester and. about 0.1% or less of the montan wax beingpreferred.

In accordance with the present invention, the wax crystal modifyingmaterial is added to a wax bearing oil, and the oil then chilled withresultant precipitation of wax in a form which is found to facilitateseparation by centrifuging or cold settling, and is also found tomaterially increase filtration rates and give other advantageous resultswhere the wax is separated by filtration. Thus the use of the dewaxingaid gives an improved yield of dewaxed oil, a denser or more compact waxcake, a higher percentage of paraffin in the slack wax, and a slack waxof higher melting point.

The dewaxing aid is preferably employed in conjunction with a dewaxingsolvent or solvent mixture. Various solvents can be used for thispurpose, including the well known and conventional dewaxing solvents andsolvent mixtures. Very satisfactory results are secured by the use of amixture of a. wax anti-solvent and an oil solvent, such as a. mixture ofacetone and benzol, methyl ethyl ketone and benzol, methyl ethyl ketoneand isopropyl ether, acetone with benzol and toluol, and the like. Inthe case of methyl ethyl ketone-benzol or methyl ethyl ketone-isopropylether, generally a proportion of about 40-60% methyl ethyl ketone to60-40% benzol or isopropyl ether is satisfactory.

The oil to be dewaxed is diluted with the dewaxing solvent or solventmixture generally in the dilution ratio of about two parts of solvent toone of oil up to about four or five parts of solvent to one of oil,although a smaller dilution ratio may be employed in certain instances.The polysaccharide ester, or the ester with montan stripping ofi thesolvent.

wax, is preferably dissolved in a small proportion of the lubricatingoil at elevated temperatures up to about 300 F. to form a concentratethereof. This concentrate is then added to the diluted wax bearing oilcharge which may be at a lower temperature, say of the order of 120 F.In order to assure proper solution of the dewaxing aid so that it givesmaximum effined Mid-Continent distillate oil of about S. A. E.

rating having a Saybolt viscosity of 67.3 at

210 F. A run was also made on the blank oil without dewaxing aid forcomparative purposes. The solvent employed was with a mixture of methylethyl ketone and 50% isopropyl ether, or 40% methyl ethyl ketone withbenzol, as indicated in the following table:

fectiveness, the diluted wax bearing oil containing the dewaxing aid maybe heated to a supersolution temperature, or to a temperaturesubstantially above the temperature of complete solution of oil insolvent, the latter being gen. erally about -140 F. Thus, the mix may beheated to a temperature of about -190 F. or to a temperature ofapproximately 20-? F. above the temperature of complete solution of oilin solvent. This is found to uniformly give im-. proved filtration ratesand yields of dewaxed oil. The mix is then chilled to a dewaxingtemperature of the order of .10 to 15 F. and the precipitated waxseparated from the oil. This is preferably accomplished by filtration,such as on continuous rotary filters, although intermittent pressurefilters may be used with advantageous results. The dewaxed oil is thenstripped to remove the solvent and the recovered solvent is recycled forthe dewaxing of additional oil. The bulk of the dewaxing aidprecipitating along with the wax and remaining in the slack wax may berecovered therefrom for reuse in the process.

By way of example, a cellulose stearate was prepared in accordance withthe method of Von G. Kita et al. as described in Kunststoffe, March1926. In this process, cotton paper or fibre was refluxed with stearylchloride in a pyridine and benzene solution for a substsantial period oftime, and the solvents then distilled off. The residue was extractedwith benzene to dissolve the cellulose stearate, and this recovered byThis cellulose stearate was used alone and also in conjunction withmontan wax in the dewaxing of a furfural re-L From the above table, itis noted that the polysaccharide ester, either alone or in conjunctionwith montan wax, gave markedly improved results with respect to filterrate, yield of Wax-v free oil and percent. of paraifin in the slack wax,produced a slack wax of higher melting point, and gave a wax cake ofgreater reduced weight indicating a more compact cake which issubstantially reduced in occluded oil content. The dewaxing aid of thisinvention is also advantageous in that it does not discolor a pale oil.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made with-out departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

1. In the dewaxing of mineral oil, the method which comprises adding tothe oil to be dewaxed a small proportion of montan wax and a higherfatty acid ester of cellulose, chilling the oil to precipitate wax, andseparating the precipitated Wax from the oil.

2. The method of claim 1, in which the said ester is selected from thegroup consisting of stearates, palmitates and oleates.

3. The method of claim 1, in which the said ester is cellulose stearate.

4. In the dewaxing which comprises adding to the oil to be dewaxed about0.1-0.5% of cellulose stearate and about 0.02-0.20% of montan wax,chilling the oil to precipitate wax, and separating the precipitated waxfrom the oil.

'EDWIN C. KNOWLES.

of mineral oil, the method

